A. Field of the Invention
The present invention relates to a new and improved cartridge filter.
B. Description of the Prior Art
In many fluid systems, the working fluid is recycled through a filter so that foreign matter present in the fluid will not accumulate and clog or damage motors or other operating mechanisms. In order to purify the fluid, filter elements or strainers may be connected to a fluid line communicating with the fluid system. The utilization of two filter elements in a concentric arrangement is highly satisfactory for systems having large filtering demands.
An example of a typical prior art filter element using concentric filter elements is disclosed in U.S. Pat. No. 3,211,292. The device disclosed in that patent includes two concentric filter or strainer elements enclosed within a housing. This device employs rigid elements supporting each filter to prevent collapse due to the forces resulting from the pressure drop across the filter elements. The rigid support elements maintain the filter elements in a proper configuration while delimiting a passage for flow of filtered fluid to the outlet of the strainer. Since each support element must have strength and rigidity to resist the total force to which one filter element is subjected, this prior art strainer suffers from disadvantages including undesirable complexity in assembly and manufacturing, and high cost.
Another prior art device employed to overcome the problem of collapsing of filter elements due to the application of inlet pressure on opposing surfaces of concentric filter elements is illustrated in U.S. Pat. No. 3,420,377. In the device disclosed in that patent, concentric filter elements are positioned such that adjacent surfaces of the filter elements are abutting, thereby supporting each element against deformation due to the influence of the equal and opposite forces resulting from the pressure drop across the elements. Filters of this type suffer from clogging and reduced flow since there is no defined channel between the two filter elements through which filtered fluid may flow to the filter outlet. The fluid must flow between the folds of the inner filter element and these folds necessarily define narrow passages allowing buildup of foreign matter. In addition, the reduced cross-sectional area of the folds limits the fluid flow rate and reduces the capacity of the device.
A problem similar to those discussed above exists if only one filter element is used. With one filter element fluid at inlet pressure acts against one surface of the filter element and can crush the filter element unless a rigid support member is provided.